water & growth on top of my water heater - replace or repair?

All,
This morning my wife reminded me to flush the sediment out of our water heater. Municipal (N. County San Diego) water is very hard and we get tons of white sediment in our faucets. To my surprise, after a year, very little sediment came out. Upon further inspection, I appear to have bigger issues on top of the water heater. Pics below.

Anyone know what this is? Almost looks like growth you see near geysers - like there's calcium in steam and the deposits create a very organic looking structure. There's also a small puddle of water on top - from steam or condensation I'm not sure. Lastly, the pressure relief valve may have an issue, because the pipe drains to the outside, and voila... there's water there too - nice and copper green. A bunch of pics below. If anyone can help me determine if this is worth my time to fix, or if I should just rip it out and replace the whole thing, I'd be grateful.

Time to replace the WH before it springs a bigger leak. I can't tell for sure, but does that label indicate 1991? If it does, that's WAY beyond the normal lifespan of a WH...you got your money's worth out of it.

Some or all of that corrosion/salt-formation may be from flue spillage/backdrafting condensation, or it may just be seepage.

Either way, the venting on both the furnace (or boiler) and the water heater doesn't look like it's very well sealed, and it's not clear that there is even any slope to the run from the water heater to where it tees into the stack. Sealing the seams & joints with furnace cement (or automotive exhaust sealer/water-glass type putty.) Whether you're replacing the thing or not, sealing the stack for maximum draw, then checking it for backdrafting is important.

In temperate Carlsbad CA the duty-cycle on the furnace is pretty low, and if the main flue is too big for the BTU output of the water heater alone to maintain good draw you may have backdrafting and /or flue condensation issues even WITH the tin sealed up, This is commonly referred to as the "orphaned water heater" issue. Sometimes it's easier/cheaper to install a power-drafted water heater (vented out the side, not the flue) than running a separate right-sized B-vent for just the water heater.

Thanks Dana.
I didn't check before I started taking everything apart, but when I put it all back together again, I sealed up all the cracks and crevices with foil tape. I used a blown out match to check the draft, and now it definitely pulls a draft into the vent stack.

Have you now changed out the water heater, or merely fixed it up a little?

Perhaps post pics showing both(?) appliances and how the common vent leaves that room/space?

A drain pan might be a good idea.

The pump appears to be blocking access to the burner cover - what is the pump "doing"?

The drain-off valve appears to be blocking easy access to the gas isolator.

Insulation should begin 18" from the nipples.

Has the T&P been installed in the Anode port? Is there a port on the side of the W/H? Is it plugged or being used for something else?

As mentioned by others, there are definitely issues with the venting.
The common vent appears to be too large and the connection should be made with a wye branch not a tee branch. The fitting where the connection is made - increaser/reducer(?) - also appears to be problematic.

Suggest that a professional eye be cast over the whole venting arrangement from appliances to terminal.

Best practice suggests that (if there is headroom) the vent(s) should rise 36" before turning.

What maintenance condition is the FAU in?

Dana,

in Ca.most metal tapes sold by plumbing supplies are high temp rated and good to go.

It's important to be pretty specific about the tape when applying it to single-wall vent. Most "high temperature" aluminum tapes are only good to 300F (often less) which is likely to fail in this app. The 3M 433 series is the only one I know of that might cut it, since its good to ~600F. I'm not sure which other tapes are out there would actually work in this application??? (I'd think 500F would be the minimum service temp to be considered a candidate here.)

You can insulate it, but not with a flammable insulation. Fiberglass or rock wool wrapped in high-temp foil tape would be fine, closed cell foam as depicted not so much.

The gases in the vent stack under normal operation are well above the service temp of any closed cell pipe insulation, and under some conditions will exceed it's melting or kindling temperature (varies by polymer type.) The gases coming out of the water heater itself are even hotter, but diluted by the room air by the time it's in the vent piping, making the stack temp somewhat cooler. If the stack is blocked or backdrafting, you get the full blast of less-diluted exhaust pouring across the top of the tank.

It's quite possible that it's venting properly when the water heater is firing, with the spillage onto the water heater occurring primarily when the other bigger-burner appliance is running. It's also possible that your house is tight enough that any time the clothes dryer and kitchen exhaust fans are running at the same time it back-drafts. Any time there is any suspicious symptom like what you see in the pictures it's worth testing it under different modes, but get it looking sorta-code-legal first: Replace the tee with a wye into the common flue, seal all seams & joints, peel back the insulation so that even if it backdrafts the hot gases won't be blowing directly onto the insulation.